This invention relates to a semiconductor wafer dividing method for dividing a semiconductor wafer, especially a thin semiconductor wafer, into many semiconductor chips. More particularly, the invention relates to a semiconductor wafer dividing method for dividing a semiconductor wafer along streets, which are arranged in a lattice fashion on the face side of the semiconductor wafer, into many semiconductor chips.
As is well known among people skilled in the art, the production of a semiconductor device requires that a nearly disc-shaped semiconductor wafer be divided into many rectangular semiconductor chips. Streets arranged in a lattice fashion are present on the face side of the semiconductor wafer, and these streets demarcate many rectangular areas. In each of the rectangular areas, a circuit is disposed. The semiconductor wafer is divided along the streets, whereby each of the many rectangular areas is formed into a semiconductor chip.
A typical method for dividing the semiconductor wafer along the streets is the use of a dicer. A dicer has a disc-shaped rotating blade, which is relatively moved along the streets to cut the semiconductor wafer along the streets. Recently, a considerably thin (e.g., 50 xcexcm or less) semiconductor wafer has often been used. If the semiconductor wafer is thin, the semiconductor wafer dividing method using a dicer involves the following problems: When the thin semiconductor wafer is cut with the rotating blade, a tiny nick tends to be made in the cut edge, and stress tends to remain in the cut edge portion. Such a nick and/or stress may decrease the strength of the resulting semiconductor chip. Even if an external force or thermal shock acting on the semiconductor chip is relatively small, the semiconductor chip may be broken.
A method for dividing a semiconductor wafer by etching, instead of cutting with a rotating blade, has also been proposed. With this dividing method, a photoresist is formed on the face side of the semiconductor wafer. Then, the photoresist is exposed to light along streets, and the photoresist is removed along the streets. Then, the semiconductor wafer is subjected to etching, whereby the semiconductor wafer is selectively etched along the streets. As a result, the semiconductor wafer is divided along the streets. According to this method, a tiny nick and/or stress can be avoided. However, this method requires that a photomask for exposure of the photoresist along the streets be kept on hand for each of various semiconductor wafers. For this and other reasons, the expenses for the division of the semiconductor wafer are considerably high. If a pattern formed of a substance, which substantially cannot be etched, is produced on the streets, such a pattern inhibits etching along the streets. This makes it impossible to apply a dividing method using etching. In the case of a semiconductor wafer made of silicon, for example, if a pattern formed from a metal such as copper or aluminum is present on the streets, an etching process exclusive to silicon cannot etch the metal forming the pattern.
A principal object of the present invention is to provide a novel and improved method which can produce a semiconductor chip by dividing a semiconductor wafer along streets, without causing a tiny nick and/or stress to decrease the strength of the resulting semiconductor chip, and without requiring a relatively expensive photomask.
Another object of the invention is to provide a novel and improved method which can divide a semiconductor wafer as required, even if a pattern formed from a substance, which cannot be etched, is present on the streets.
To attain the principal object, the present invention performs a unique physical removal step of physically removing a resist, which has been formed on the face side of a semiconductor wafer, in areas extending along streets.
As a semiconductor wafer dividing method for attaining the principal object, the invention provides a semiconductor wafer dividing method for dividing a semiconductor wafer, on whose face side many rectangular areas are demarcated by streets arranged in a lattice fashion, along the streets to convert each of the many rectangular areas into a semiconductor chip, comprising:
a masking step of forming a resist on the face side of the semiconductor wafer;
a physical removal step of physically removing the resist in areas extending along the streets after the masking step; and
an etching step of applying an etching process to the semiconductor wafer after the physical removal step to etch the semiconductor wafer along the streets.
In the physical removal step, it is preferred to cut the resist along the streets by means of a disc-shaped rotating blade. The remaining object is attained by removing not only the resist, but also a pattern formed from a substance, which cannot be etched, in the areas extending along the streets in the physical removal step. In a preferred embodiment, the semiconductor wafer has a thickness of 50 xcexcm or less, and the resist has a thickness of 5 to 15 xcexcm.